Lubricated system comprising a DLC surface

Abstract

The present invention relates to a lubricated system comprising: a) a component comprising a first surface which is a diamond-like carbon (DLC) surface; b) a component comprising a second surface; and c) a lubricant formulation interposed between the first surface and second surface. The lubricant formulation comprises: i) a base stock; ii) a molybdenum compound; iii) an organic polymer comprising a hydrophobic polymeric sub unit selected from polyesters and functionalised polyolefins and a hydrophilic polymeric sub unit selected from polyethers; and iv) optionally, other additives. The combination of the molybdenum compound and the organic polymer in the lubricant formulation reduces the wear on one or more of the surfaces in the lubricated system when compared with using the molybdenum containing friction modifier alone.

The invention claimed is: 
     
       1. A lubricated system comprising:
 a) a component comprising a first surface which is a diamond-like carbon (DLC) surface; 
 b) a component comprising a second surface; and 
 c) a lubricant formulation interposed between the first surface and second surface, wherein the lubricant formulation comprises:
 i) a base stock; 
 ii) 0.05 to 5 wt % of the lubricant formulation of a molybdenum compound comprising a molybdenum dithiocarbamate (MoDTC); 
 iii) 0.05 to 5 wt % of the lubricant formulation of an organic polymer comprising a hydrophobic polymeric sub unit comprising a polyisobutylene functionalized to comprise a diacid and/or anhydride group and a hydrophilic polymeric sub unit comprising a polyethylene glycol having a number average molecular weight of 400 to 1000 daltons; and 
 iv) optionally, other additives, 
 
 wherein the lubricant formulation reduces kinetic coefficient of friction by at least 5% and reduces wear of the first and/or second surface by at least 50% during operation of the lubricated system when compared with an equivalent lubricant formulation which does not comprise the molybdenum compound and the organic polymer. 
 
     
     
       2. A lubricated system according to  claim 1  wherein the second surface is a metal surface. 
     
     
       3. A lubricated system according to  claim 1  wherein the lubricated system is an automotive engine. 
     
     
       4. A lubricated system according to  claim 1  wherein the hydrophobic polymeric sub unit comprises a polyisobutylene succinic anhydride. 
     
     
       5. A lubricated system according to  claim 1  wherein the organic polymer further comprises a polyol. 
     
     
       6. A lubricated system according to  claim 5  wherein the polyol is selected from glycerol, polyglycerol, neopentyl glycol, trimethylolethane, trimethylolpropane, trimethylolbutane, pentaerythritol, dipentaerythritol, tripentaerythritol, sucrose, sorbitan, sorbitol and mixtures thereof. 
     
     
       7. A lubricated system according to  claim 1  wherein the organic polymer is a friction reducing additive. 
     
     
       8. A method of reducing wear in a lubricated system by at least 50% and kinetic coefficient of friction by at least 5% during operation of the lubricated system, wherein the lubricated system comprises a component with a DLC surface and wherein the method comprises the steps of:
 a. providing a lubricant formulation to contact the DLC surface; 
 b. providing 0.05 to 5 wt % of the lubricant formulation of a molybdenum compound comprising a molybdenum dithiocarbamate (MoDTC) in the lubricant formulation to reduce friction in the lubricated system; and 
 c. providing 0.05 to 5 wt % of the lubricant formulation of an organic polymer comprising a hydrophobic polymeric sub unit comprising a polyisobutylene functionalized to comprise a diacid and/or anhydride group and a hydrophilic polymeric sub unit comprising a polyethylene glycol having a number average molecular weight of 400 to 1000 daltons in the lubricant formulation to reduce the rate of wear and friction of the DLC surface during operation of the lubricated system.